The present invention relates to a timekeeping system in which timing of a start signal for notifying competitors is made coincident with timing of start of timekeeping in a speed competition, for example.
A system block diagram according to a conventional technique is shown in FIG. 3. Conventionally in speed competitions, a start signal transmission device 14 for notifying competitors of start timing and a timekeeping device 15 for measuring goal line passing time are independent in processing of a competition start signal. A start signal emitted by a start pistol 1 is passed through a buffer circuit 4 and then distributed to two systems. One is that the start signal is distributed by a start signal distributor circuit 5 to activate a speaker 2 and a luminous portion of the start pistol 1, competitors being thus notified of start by sound and light signals. The other one is that the start signal passed through the buffer circuit 4 is transmitted to the timekeeping device 15 via a transmission cable 6. Upon receiving this signal, a counter circuit 10 begins to count clock pulses of a reference timer 8 included in the timekeeping device.
In this scheme, however, the reference timer 8 included in the timekeeping device serves as a frequency divider for output of a reference quartz oscillator 9 and generates clock pulses. The counter circuit 10 counts the clock pulses to derive elapsed time from the competition start. Since the start signal emitted from the start pistol 1 is not in synchronism with the clock pulses derived by dividing the frequency of the reference quartz oscillator 9, as shown in FIG. 2, a start signal of a waveform (C) is delayed by a time t.sub.e corresponding to at most one clock of clock pulses generated by the reference timer having a waveform (B) in comparison with the start signal of a waveform (A) issued by the start pistol 1.
Assuming now that the clock pulse derived from the frequency divider has a period of 1 ms and measurement is made by using the conventional scheme, an error of at most 1 ms is caused between the time whereat competitors know the start by means of a sound or light signal and the result of time measurement.
Furthermore, if this timekeeping device has an electronic slit camera for taking line images of competitors passing over the goal line by using a linear sensor 17, the linear sensor is scanned in synchronism with the reference timer clock supplied from the reference timer 8. In the same way as the result of time measurement, therefore, an error of at most 1 ms is caused in the images taken for decision as well.
Furthermore, the system for the speaker 2 and the luminous portion of the start pistol 1 is independent of the system for transmitting the start signal to the timekeeping device via the transmission cable 6. Therefore, even if the start signal should not be transmitted because of abnormality on the transmission cable 6 for the timekeeping device such as breaking of a wire, competitors start in response to the sound and light signals generated by the start signal transmission device 14. Thus there is a risk of running a race without measuring the goal time.